Metal catalyst, method for manufacturing the metal catalyst and electrochemical reduction method

ABSTRACT

This invention relates to a metal catalyst, a manufacturing method of the metal catalyst, and an electrochemical reduction method. 
     The metal catalyst is manufactured by a method comprising providing a conductor to one side of an insulator, providing a fluid including a metal ion and an electron mediator to the other side of the insulator and providing a voltage to the conductor. 
     The electrochemical reduction method comprises providing a conductor to one side of an insulator, providing a fluid including reduction material and an electron mediator to the other side of the insulator and providing a voltage to the conductor.

BACKGROUND

1. Technical Field

The present disclosure relates to a metal catalyst, a manufacturingmethod of the metal catalyst, and an electrochemical reduction method.

2. Description of the Related Art

Metal catalysts are used in the various fields. For example, the metalcatalyst can be used for a synthesis reaction or for pollutantdegradation. Recently, a nano-sized metal catalyst is developed so thathigh selectivity can be implementable in the lower temperature with thenano-sized metal catalyst, compared to the conventional metal catalysts.However, the nano-sized metal catalyst is supported by an inert solidsupport for anti-aggregation and reuse. In order to form metal catalystof nanoparticles on the inert solid support directly, the process iscomplicated and the cost is greatly increased.

SUMMARY

Example embodiments provide a metal catalyst manufactured by anelectrochemical reduction method.

Example embodiments also provide a manufacturing method for a metalcatalyst using by an electrochemical reduction method.

According to one aspect of example embodiments, a metal catalystmanufactured by a method comprises providing a conductor to one side ofan insulator, providing a fluid including a metal ion and an electronmediator to the other side of the insulator and providing a voltage tothe conductor.

In some embodiments, the metal catalyst may comprise a crystal structurewith a miller index of (hkl), and at least one of the h, k and l is morethan 2.

In some embodiments, the metal catalyst may have a polygonal shape.

In some embodiments, the metal catalyst may comprise two or more kindsof metals.

In some embodiments, the metal ion may comprise one or more chosen frompalladium, gold, platinum, copper, and cobalt.

In some embodiments, the electron mediator may comprise one or morechosen from a hydrogen ion, a hydrogen atom and a hydrogen molecule.

In some embodiments, the fluid may comprise a solution or a gas. Thesolution may comprise an aqueous solution or an organic solution, andthe gas may include hydrogen gas.

In some embodiments, the conductor may comprise a semiconductor or ametal doped by an n-type dopant or a p-type dopant.

In some embodiments, the insulator may be a dielectric layer. Theinsulator may comprise a semiconductor oxide, a metal oxide, asemiconductor nitride, a metal nitride or a polymer.

In some embodiments, the insulator may have a thickness of about 0.5 nmto about 100 μm.

According to another aspect of example embodiments, a method formanufacturing a metal catalyst comprises providing a conductor to oneside of an insulator, providing a fluid including a metal ion and anelectron mediator to the other side of the insulator and providing avoltage to the conductor.

In some embodiments, the insulator may comprise a functional groupreacting and combining with the metal ion at a surface of the insulatorcontacting with the solution. The functional group may include an aminegroup or a sulfur group.

According to another aspect of example embodiments, an electrochemicalreduction method comprises providing a conductor to one side of aninsulator, providing a fluid including reduction material and anelectron mediator to the other side of the insulator and providing avoltage to the conductor.

In some embodiments, the electron mediator may move into the insulatorby the voltage and receive electrons from the conductor and provide theelectrons to the reduction material.

In some embodiments, the electron mediator may comprise one or morechosen from a hydrogen ion, a hydrogen atom and a hydrogen molecule.

In some embodiments, the fluid may comprise a solution or a gas. Thesolution may comprise an aqueous solution or an organic solution, andthe gas may include hydrogen gas.

In some embodiments, an electric current may flow in the insulator bythe voltage, and the size of the electric current may be adjusted by apH of the solution.

In some embodiments, the conductor may comprise a semiconductor or ametal doped by an n-type dopant or a p-type dopant.

In some embodiments, the insulator may be a dielectric layer. Theinsulator may comprise a semiconductor oxide, a metal oxide, asemiconductor nitride, a metal nitride or a polymer.

In some embodiments, the insulator may have a thickness of about 0.5 nmto about 100 μm.

According to the embodiments of the present invention, anelectrochemical reduction method is a simple process and can save a lotof costs. Moreover, the electrochemical reduction method is eco-friendlybecause neither a surfactant nor a stabilizer is used, unlike a chemicalreduction method. Moreover, a carbon dioxide or oxygen may be reduced bythe electrochemical reduction method. Moreover, with a simple process, ametal catalyst can be formed by the electrochemical reduction method.For example, a metal catalyst supported by an insulator, a metalcatalyst in a polygonal shape, a metal catalyst having a crystalstructure with a miller index of (hkl), in which at least one of the h,k and l are more than 2, and multi-metal catalyst can be formed by theelectrochemical reduction method with a simple process. The metalcatalyst may be used effectively with a simple process in various fieldssuch as energy technology, pollution protection, and environmentpurification.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic flow chart illustrating an electrochemicalreduction method in accordance with embodiments of the presentinvention;

FIG. 2 illustrates the electrochemical reduction method of FIG. 1;

FIG. 3 is an expanded figure of the area ‘A’ of FIG. 2;

FIG. 4 illustrates a result of Surface Enhanced Raman Scatteringanalysis for an electron mediator and an insulator in accordance with anembodiment of the present invention;

FIG. 5 is a graph illustrating changes of an electric current in aninsulator according to a supply voltage;

FIG. 6 is a graph illustrating changes of an electric current in aninsulator according to a pH of a solution;

FIG. 7 is a graph illustrating changes of an onset voltage according toa pH of a solution;

FIG. 8 is a schematic flow chart illustrating a method for manufacturinga metal catalyst in accordance with embodiments of the presentinvention;

FIG. 9 illustrates the method for manufacturing the metal catalyst inFIG. 8;

FIG. 10 a is a FESEM (Field Emission Scanning Electron Microscopy) imageof a Pd—Cu nanocrystal manufactured and supported by the silicon dioxidein accordance with embodiments of the present invention;

FIG. 10 b is a high magnification FESEM image of the Pd—Cu nanocrystalin FIG. 10 a;

FIG. 10 c is a HAADF-STEM (High Angle Annular Dark Field ScanningTransmission Electron Microscopy) image of the Pd—Cu nanocrystal in FIG.10 a;

FIG. 10 d and FIG. 10 e are TEM (Transmission Electron Microscopy)images of the Pd—Cu nanocrystals in FIG. 10 a; and

FIG. 10 f illustrates electron diffraction pattern of the Pd—Cunanocrystals in FIG. 10 a.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, a detailed description will be given of embodiments of thepresent invention. The present invention is not limited to theseembodiments and may be embodied in the other forms. The embodiments ofthe present invention are provided so that thorough and completecontents are ensured and the spirit of the invention is sufficientlytransferred to a person having ordinary knowledge in the art.

<Electrochemical Reduction Method Using Electron Mediators>

FIG. 1 is a schematic flow chart illustrating an electrochemicalreduction method in accordance with embodiments of the presentinvention. FIG. 2 illustrates the electrochemical reduction method ofFIG. 1. FIG. 3 is an expanded figure of the area ‘A’ of FIG. 2.

Referring to FIG. 1 to FIG. 3, the electrochemical reduction methodincludes a step S110 of providing a conductor 110 to one side of aninsulator 120, a step S120 of providing a solution 130 includingreduction material 131 and electron mediators 135 to the other side ofthe insulator 120, and a step S130 of providing an electrical voltageinto the conductor 110.

In the step S110, the conductor 110 is provided to the one side of theinsulator 120.

The insulator 120 may be a dielectric layer. The insulator 120 mayinclude a semiconductor oxide, a metal oxide, a semiconductor nitride, ametal nitride, or a polymer. For example, the insulator 120 may includea silicon dioxide or a silicon nitride. The insulator 120 may include amaterial, which may be permeable to the electron mediators 135 by thevoltage provided to the conductor 110. Moreover, the insulator 120 mayhave a proper thickness, in which the electron mediators 135 permeatingby the voltage can function as an electron transfer mediator. Theinsulator 120 may have various thicknesses according to materials. Forexample, the insulator 120 may have the thickness of about 0.5 nm toabout 100 μm. The insulator 120 may be formed by a thermal oxidationprocess or an electrochemical oxidation process for the conductor 110.

In the present embodiment, the insulator 120 has a direct contact on theconductor 110. However, a layer or a material may be interposed betweenthe insulator 120 and the conductor 110.

In the step S120, the solution 130 is provided to the other side of theinsulator 120. The solution 130 includes the reduction material 131 andthe electron mediators 135.

The reduction material 131, for example, may include carbon dioxide oroxygen. The reduction material 131 may include various materials whichis not limited with the carbon dioxide or the oxygen.

The electron mediators 135 permeate into the insulator 120 and providesthe electrons supplied from the conductor 110 into the reductionmaterial 131 so that the reduction material 131 can be reduced. Theelectron mediators 135, for example, may be hydrogen ions H⁺.

The solution 130 may include an aqueous solution or an organic solution.In particular, the solution 130 may include an electrolyte solution.Moreover, a gas may be used instead of the solution 130. For example,the gas may include hydrogen gas

The positions of the conductor 110, the insulator 120 and the solution130 may be changeable. For example, the insulator 120 may be provided onthe conductor 110 and the solution 130 may be provided on the insulator120. Moreover, the conductor 110 having the insulator 120 may beprovided into the solution 130.

In the step S130, the voltage is provided to the conductor 110.

The voltage may be provided by a working electrode 141, a referenceelectrode 142 and a counter electrode 143. The working electrode 141 maybe electrically connected to the conductor 110, and the referenceelectrode 142 and the counter electrode 142 may be electricallyconnected to the solution 130. Moreover, the working electrode 141, thereference electrode 142 and the counter electrode 143 may beelectrically connected to the potentiostat. Otherwise, the conductor 110may be directly connected on the potentiostat and work as the workingelectrode. The reference electrode 142 may include Ag/AgCl (in 3M Nacl),and the counter electrode 143 may include a Pt wire of about 0.5 mmdiameter.

By the voltage, the hydrogen ions H⁺, which are the electron mediators135 in the solution 130, move into the insulator 120 and receiveelectrons from the conductor 110 so that the hydrogen ions H⁺ arereduced as hydrogen atoms H• and/or hydrogen molecules H₂. The hydrogenatoms H• and/or the hydrogen molecules H₂ provide electrons to thereduction material 131 in the solution 130 so that the reductionmaterial 131 is reduced. While the reduction material 131 is reduced,the hydrogen atoms H• and/or the hydrogen molecules H₂ are oxidizedagain as hydrogen ions H⁺. By the voltage supplied to the conductor 110,the hydrogen ions H⁺ move into the insulator 120 and are continuouslyreduced and oxidized in the insulator 120 so that the reduction materialis reduced. The hydrogen ions H⁺, the hydrogen atoms H• and/or thehydrogen molecules H₂ in the insulator 120 work as electron transfermediators transferring electrons from the conductor 110 to the reductionmaterial 131.

When the reduction material 131 is carbon dioxide, ethanol or formicacid may be formed after reduction. When the reduction material 131 isoxygen, water, hydrogen peroxide or hydroxyl ion may be formed afterreduction. As mentioned the above, by using the electrochemicalreduction method according to the embodiments of the present invention,the carbon dioxide or the oxygen may be reduced, and various compoundsmay be formed with reducing carbon dioxide production by a simpleprocess.

FIG. 4 illustrates a result of Surface Enhanced Raman Scatteringanalysis for an electron mediator and an insulator in accordance with anembodiment of the present invention. FIG. 4 illustrates a SurfaceEnhanced Raman Scattering spectrum which is measured by providing −1.5Vvoltage to n-type silicon substrate (n-Si/SiO₂) when gold micro bead isdisposed on a surface of the n-type silicon substrate for the SurfaceEnhanced Raman Scattering after 0.1M potassium phosphate solution isdisposed on the n-type silicon substrate including silicon dioxide of 5nm thickness.

Referring to FIG. 4, a peak is not shown in the Surface Enhanced RamanScattering spectrum when the voltage is not supplied to the n-typesilicon substrate. Then a peak is shown in the Surface Enhanced RamanScattering spectrum, at 1 second and 596 seconds after supplying −1.5Vvoltage to the n-type silicon substrate. Moreover, the peak gets greateraccording to the passage of the time after the voltage is supplied. Thepeak is shown at a vibration frequency of about 2905 cm⁻¹, which isrelated to O—H⁺.

As mentioned the above, when −1.5V voltage is supplied to the n-typesilicon substrate, the hydrogen ions or hydrogen atoms move into thesilicon dioxide and form Si—(OH⁺)—Si. The electrons of the n-typesilicon substrate may move into an interface between the potassiumphosphate solution and the silicon dioxide through the hydrogen atom ofthe Si—(OH⁺)—Si. The reduction material in the potassium phosphatesolution may be reduced by receiving electrons at the interface.

FIG. 5 is a graph illustrating changes of an electric current in aninsulator according to a supply voltage. The graph illustrates acurrent-voltage curve measured at 10 mV/s of scan speed at a roomtemperature for a system, which includes a 0.1M potassium phosphatesolution of pH 3 having 1 mM Ru(NH₃)₆Cl₃ and Ru(NH₃)₆Cl₂ and an n-typesilicon substrate (n-Si/SiO₂) having silicon dioxide of 6 nm thicknessin the solution. The silicon substrate, which was highly doped by then-type dopant, was used as the n-type silicon substrate.

Referring to FIG. 5, the current-voltage curve illustratesasymmetrically. The asymmetry means the difference of the flow of theelectrons, which is the flow of the electric current through the silicondioxide. When the negative voltage is provided, the amount of thehydrogen ions moving into the silicon dioxide is different from when thepositive voltage is provided.

When the negative voltage is provided to a system, the hydrogen ions inthe potassium phosphate solution move into the silicon dioxide andabsorb electrons from the n-type silicon substrate, and provides theelectrons to the Ru(NH₃)₆ ³⁺ in the potassium phosphate solution so thatthe Ru(NH₃)₆ ³⁺ is reduced. When the negative voltage is provided to thesystem, the hydrogen ions in the potassium phosphate solution work aselectron mediators, thus easily reducing the Ru(NH₃)₆ ³⁺ in thepotassium phosphate solution because the electrons flow well even with asmall negative voltage. However, when the positive voltage is providedto the system, very high positive voltage should be provided in order tooxidize the Ru(NH₃)₆ ³⁺ in the potassium phosphate solution because itis hard for the hydrogen ions to move to the silicon dioxide and work asthe electron mediators.

As mentioned the above, when the negative voltage is provided to thesystem, the hydrogen ions can move to the silicon dioxide and beaccumulated easier than when the positive voltage is provided to thesystem. The hydrogen ions, which move to the silicon dioxide and areaccumulated, transfer the electrons absorbed from the n-type siliconsubstrate to the reduction material in the potassium phosphate solutionso as to reduce the reduction material.

FIG. 6 is a graph illustrating changes of an electric current in aninsulator according to a pH of a solution. FIG. 7 is a graphillustrating changes of an onset voltage according to a pH of asolution. The graph illustrates a current-voltage curve measured at 10mV/s of scan speed at a room temperature when the pH of a 0.1M potassiumphosphate solution is changed to 3, 6, and 9 respectively. The onsetvoltage is defined as a voltage when a current density is a 30% of abase current.

Referring to FIG. 6 and FIG. 7, the amount of the current is increasedas the pH of the solution is decreased, and the onset voltage is shownat the smaller negative voltage. Thus, when the acidity of the solutionis stronger, the current can flow through the silicon dioxide with thesmaller voltage so that the reduction material can be reduced. Byadjusting the pH of the solution, the amount of the current can becontrolled, and the amount of voltage can be controlled.

<Method for Manufacturing Metal Catalyst Using the ElectrochemicalReduction Method and the Metal Catalyst Manufactured by the Method>

FIG. 8 is a schematic flow chart illustrating a method for manufacturinga metal catalyst in accordance with embodiments of the presentinvention. FIG. 9 illustrates the method for manufacturing the metalcatalyst in FIG. 8.

Referring to FIG. 8 and FIG. 9, the electrochemical reduction methodincludes a step S210 of providing a conductor 210 to one side of aninsulator 220, a step S220 of providing a solution 230 including metalions 231 and electron mediators 235 to the other side of the insulator220, and a step S230 of providing an electrical voltage into theconductor 210.

In the step S210, the conductor 210 is provided to the one side of theinsulator 220.

The conductor 210 may include silicon or metal doped by an n-type dopantor a p-type dopant. For example, the conductor 210 may include silicondoped by the n-type dopant.

The insulator 220 may be a dielectric layer. The insulator 220 mayinclude a semiconductor oxide, a metal oxide, a semiconductor nitride, ametal nitride or a polymer. For example, the insulator 220 may include asilicon dioxide or a silicon nitride. The insulator 220 may include amaterial, which may be permeable to the electron mediators 235 by thevoltage provided to the conductor 210. Moreover, the insulator 220 mayhave a proper thickness, in which the electron mediators 235 permeatingby the voltage can function as an electron transfer mediator. Theinsulator 220 may have various thicknesses according to materials. Forexample, the insulator 120 may have the thickness of about 0.5 nm toabout 100 μm. The insulator 220 may be formed by a thermal oxidationprocess or an electrochemical oxidation process for the conductor 210.

In the present embodiment, the insulator 220 has a direct contact on theconductor 210. However, a layer or a material may be interposed betweenthe insulator 220 and the conductor 210.

In the step S220, the solution 230 is provided to the other side of theinsulator 220. The solution 230 includes the metal ions 231 and theelectron mediators 235.

The metal ions 231, for example, may include one or more chosen frompalladium ion, gold ion, platinum ion, copper ion, and cobalt ion. Themetal ions 231 may include various ions which is not limited asmentioned the above.

The electron mediators 235 permeate into the insulator 220 and providethe electrons supplied from the conductor 210 into the metal ions 231 sothat the metal ions 231 can be reduced. The electron mediators 235, forexample, may be hydrogen ions H⁺.

The solution 230 may include an aqueous solution or an organic solution.In particular, the solution 230 may include an electrolyte solution.Moreover, a gas may be used instead of the solution 230. For example,the gas may include hydrogen gas.

The positions of the conductor 210, the insulator 220 and the solution230 may be changeable. For example, the insulator 220 may be provided onthe conductor 210 and the solution 230 may be provided on the insulator220. Moreover, the conductor 210 having the insulator 220 may beprovided into the solution 230.

In the step S230, the voltage is provided to the conductor 210.

The voltage may be provided by a working electrode, a referenceelectrode and a counter electrode, which are not shown in the figuresrelated to the present embodiment. The working electrode may beelectrically connected to the conductor 210, and the reference electrodeand the counter electrode may be electrically connected to the solution230. Moreover, the working electrode, the reference electrode and thecounter electrode may be electrically connected to a potentiostat (notshown).

By the voltage, the hydrogen ions which are the electron mediators 235in the solution 230, move into the insulator 220 and receive electronsfrom the conductor 210 so that the hydrogen ions H⁺ are reduced ashydrogen atoms H• and/or hydrogen molecules (not shown). The hydrogenatoms H• and/or the hydrogen molecules provides electrons to the metalions 231 in the solution 230 so that the metal ions 231 are reduced.While the metal ions 231 are reduced, the hydrogen atoms H• and/or thehydrogen molecules are oxidized again as hydrogen ions H⁺. By thevoltage supplied to the conductor 210, the hydrogen ions H⁺ move intothe insulator 220 and are continuously reduced and oxidized so that themetal ions 231 are reduced. The hydrogen ions the hydrogen atoms H•and/or the hydrogen molecules in the insulator 220 work as electrontransfer mediators transferring electrons from the conductor 210 to themetal ions 231.

The metal ions 231 may be reduced and form a metal catalyst 232 on asurface of the insulator 220. The metal catalyst 232 may be adhered tothe surface of the insulator 220 and be supported by the insulator 220.The metal catalyst 232 may be formed as a nanoparticle or a nanocrystal.Moreover, the metal catalyst 232 may have a crystal structure with amiller index of (hkl), and at least one of the h, k and l is more than2, and the metal catalyst 232 may have a polygonal shape. Thus, themetal catalyst 232 may have an excellent catalytic activity.

The insulator 220 may include a functional group, which can react andcombine with the metal ions 231, at the surface contacting with thesolution 230. The functional group may include an amine group or asulfur group. The metal catalyst 232 is more strongly adhered andcombined to the surface of the insulator 220 by the functional group.

The metal ions 231, for example, may include palladium ions Pd²⁺. Thepalladium ions Pd²⁺ are reduced by the hydrogen atoms H• and/or thehydrogen molecules in the insulator 220 so that a palladium particle ora palladium crystal may be formed on the surface of the insulator 220.The hydrogen atoms H• and/or the hydrogen molecules in the insulator 220move to the surface of the palladium particle or crystal, and thereduction of the palladium ions Pd²⁺ keeps to proceed at the surface.Thus, the palladium particle or crystal grows so that the palladiumcatalyst Pd can be formed.

When the solution 230 may include two or more kinds of metal ions 231, amulti-metal catalyst 232 may be formed. For example, when the solution230 includes palladium ions Pd²⁺ and copper ions Cu²⁺, the palladiumions Pd²⁺ are reduced and the palladium particle or crystal, which hasmore strong bonding force with the insulator 230, is formed on thesurface of the insulator 220. The copper ions Cu²⁺ are reduced by thehydrogen atoms H• and/or the hydrogen molecules, which moved from theinsulator 220 to the surface of the palladium particle or crystal. Thus,the bimetal catalyst 232 with palladium and copper may be formed.

In the present embodiment, the metal catalyst 220 is formed at thesurface of the insulator 220. However, the position for forming themetal catalyst 220 is not limited to the surface of the insulator 220.The metal catalyst 220 may be formed in the solution 230. For example,the metal catalyst such as Cu nanoparticles, may be formed in thesolution 230.

FIG. 10 a is a FESEM image of a Pd—Cu nanocrystal manufactured andsupported by the silicon dioxide in accordance with embodiments of thepresent invention. FIG. 10 b is a high magnification FESEM image of thePd—Cu nanocrystal in FIG. 10 a. FIG. 10 c is a HAADF-STEM image of thePd—Cu nanocrystal in FIG. 10 a. FIG. 10 d and FIG. 10 e are TEM imagesof the Pd—Cu nanocrystal in FIG. 10 a. FIG. 10 f illustrates electrondiffraction pattern of the Pd—Cu nanocrystal in FIG. 10 a.

The Pd—Cu nanocrystal is formed by providing −1.3V constant voltageduring 30 minutes when the n-type silicon substrate is dipped in 0.1MH₂SO₄ solution including 1 mM CuSO₄ after providing −1.2V constantvoltage during 30 minutes to the n-type silicon substrate having thesilicon dioxide in 0.1M potassium phosphate solution of pH 3 including 1mM PdCl₂.

Referring to FIG. 10 a to FIG. 10 f, the Pd—Cu nanocrystal may have apolygonal shape such as an octahedron or a triangular prism. Moreover,the Pd—Cu nanocrystal may have a crystal structure, the miller index ofwhich is (hkl), and at least one of h, k and l are more than 2.

As mentioned the above, according to the embodiments of the presentinvention, a multi-metal catalyst as well as a single metal catalyst canbe formed at a room temperature by an electrochemical reduction method,which is simple process. Moreover, the metal catalyst is supported by aninsulator or separated from the insulator, and can be used simply andeffectively in the various field such as an energy technique, pollutionprevention and environment purification.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A metal catalyst manufactured by a methodcomprising: providing a conductor to one side of an insulator; providinga fluid including a metal ion and an electron mediator to the other sideof the insulator; and providing a voltage to the conductor.
 2. The metalcatalyst of claim 1, wherein the metal catalyst comprises a crystalstructure with a miller index of (hkl), and at least one of the h, k andl is more than
 2. 3. The metal catalyst of claim 1, wherein the metalcatalyst has a polygonal shape.
 4. The metal catalyst of claim 1,wherein the metal catalyst comprises two or more kinds of metals.
 5. Themetal catalyst of claim 1, wherein the metal ion comprises one or morechosen from palladium, gold, platinum, copper and cobalt.
 6. The metalcatalyst of claim 1, wherein the electron mediator comprises one or morechosen from a hydrogen ion, a hydrogen atom and a hydrogen molecule. 7.The metal catalyst of claim 1, wherein the fluid comprises a solution ora gas, the solution comprises an aqueous solution or an organicsolution, and the gas comprises hydrogen gas.
 8. The metal catalyst ofclaim 1, wherein the conductor comprises a semiconductor or a metaldoped by an n-type dopant or a p-type dopant.
 9. The metal catalyst ofclaim 1, wherein the insulator is a dielectric layer, and the insulatorcomprises a semiconductor oxide, a metal oxide, a semiconductor nitride,a metal nitride or a polymer.
 10. The metal catalyst of claim 1, whereinthe insulator has a thickness of about 0.5 nm to about 100 μm.
 11. Amethod for manufacturing a metal catalyst, comprising: providing aconductor to one side of an insulator; providing a fluid including ametal ion and an electron mediator to the other side of the insulator;and providing a voltage to the conductor.
 12. The method formanufacturing a metal catalyst of claim 12, wherein the insulatorcomprises a functional group reacting and combining with the metal ionat a surface of the insulator contacting with the solution.
 13. Anelectrochemical reduction method, comprising: providing a conductor toone side of an insulator; providing a fluid including reduction materialand an electron mediator to the other side of the insulator; andproviding a voltage to the conductor.
 14. The electrochemical reductionmethod of claim 13, wherein the electron mediator moves into theinsulator by the voltage and receives electrons from the conductor andprovides the electrons to the reduction material.
 15. Theelectrochemical reduction method of claim 13, wherein the electronmediator comprises one or more chosen from a hydrogen ion, a hydrogenatom and a hydrogen molecule.
 16. The electrochemical reduction methodof claim 13, wherein the fluid comprises a solution or a gas, thesolution comprises an aqueous solution or an organic solution, and thegas comprises hydrogen gas.
 17. The electrochemical reduction method ofclaim 16, wherein an electric current flows in the insulator by thevoltage, and the size of the electric current is adjusted by a pH of thesolution.
 18. The electrochemical reduction method of claim 13, whereinthe conductor comprises a semiconductor or a metal doped by an n-typedopant or a p-type dopant.
 19. The electrochemical reduction method ofclaim 13, wherein the insulator is a dielectric layer, and the insulatorcomprises a semiconductor oxide, a metal oxide, a semiconductor nitride,a metal nitride or a polymer.
 20. The electrochemical reduction methodof claim 13, wherein the insulator has a thickness of about 0.5 nm toabout 100 μm.